A water purification device of this kind is known from U.S. Pat. No. 6,139,740. By means of the fluid pump, the fluid is pumped to the primary side under a relatively high pressure. According to the principle of reverse osmosis, the water then penetrates to the secondary side. During this penetration, the water is demineralised or purified. In order to simplify the following explanation, the water on the secondary side is merely called “secondary side water”.
The secondary side water is usually collected in a tank, from which it is at the disposal of the consumer. The consumer then has the possibility of tapping the required amount of secondary side water on need.
In some applications, however, the consumer requires the secondary side water under a higher pressure. An example of such an application is a spraying system, with which plants can be irrigated. To enable the spraying of the secondary side water through orifices, higher pressures are required, for example more than 30 bar. A usual spraying pressure for secondary side water is even 70 bar. Another example of the application of secondary side water is the so-called water hydraulics, whose components are sold under the name of “NESSIE” by Danfoss A/S, Nordborg, Denmark.
In order to bring the secondary side water to the desired higher pressure, one or more pumps are used, which are arranged between the hold tank on the secondary side of the diaphragm unit and the consumer. This pump brings the secondary side water to the desired higher pressure. However, it has turned out that with demineralised water the required water pumps have a relatively short life. The life is substantially shorter than with the use of “normal” or unpurified water. Even with saltwater the life is longer.